Do you mean garden soil or potting compost? If it's potting compost you intend using the bag gives the hazard warning on the side . As for mess .. go for your life. Too many kids do not get enough of that type of tactile experience at home so getting dirty in school is a therapeutic treat. In warmer weather I have put a large lump of dried clay in a water trough and they move it around, break it up, etc. Kids need to wear an apron to avoid staining clothes - but they have the best fun.

We had a dinosaur topic recently and because of building work going on in our outdoor area, our outdoor activities were seriously curtailed. Anyway, I brought a load of the soil, from our digging area, into the class and dumped it into a tuff spot for the children to create a dinosaur landscape.
Some of the children turned up at school with lumps which, they were told, were bites and blamed the soil (the same soil the children played with every day outside, btw) and the head advised us to get rid of it.
Amazingly, since playing with the soil outdoors again, no-one has been bitten. And curiously, the parents have stopped complaining about having to wash little Johnny's sweatshirt every night because of the dried on mud...

Thanks for all replies. Don't know what's happening this year but I have the fussiest parents ever- am fed up with having to explain why kids are messy- it washes off and they are really having a great time whilst getting loads out of it. am looking forward to soil exploration!!!!